When burners for fluid fuels are provided as high speed burners with an output of approximately 100.000.000 Kcal/m.sup.3 h considerable thermal problems arise. Although the combustion chamber is cooled at its outer surface by the combustion air this cooling is not sufficient at higher loads so that usually a ceramic lining must be provided. Such lining increases the price of the burner and has the disadvantage that in some fields of application, f.i. burning of waste, the lining is attacked by the salts generated by the combustion such as sodium compounds and vanadium compounds. Besides this, high speed burners often suffer from starting difficulties which necessitate expensive start or pilot burners instead of the usual spark electrodes.